One currently very active area of glass research has centered around the production of optical waveguides. This research has involved the development of new glass compositions and production techniques to improve the transmission (reduce the attenuation) thereof. One branch of the composition research has concentrated upon glasses demonstrating high transmission in the infrared region of the radiation spectrum. Hence, because attenuation decreases approximately with the fourth power of wavelength, the greater the infrared transmission the lower the loss.
Considerable effort has been expended in developing oxide-free glasses, e.g., fluoride and chalcogenide compositions, which do indeed transmit infrared radiation at long wavelengths. However, those glasses are frequently quite susceptible to surface deterioration in service, are relatively unstable to devitrification, and exhibit high coefficients of thermal expansion. Furthermore, added care must be employed in melting and forming those compositions. Consequently, research has continued to discover glass compositions capable of being melted and formed utilizing apparatus and techniques conventional in the commercial manufacture of glass products.
U.S. Pat. No. 3,723,141 briefly reviews oxide-containing glass compositions disclosed in the prior art stated to display good transmission of infrared radiation. It was there observed that those glasses of the prior art manifested good transmission only to wavelengths to about six microns. The patent, itself, described glass compositions which transmitted significant amounts of infrared radiation at wavelengths longer than six microns. The patented glasses had compositions within the PbO--Bi.sub.2 O.sub.3 system and consisted essentially, in weight percent on the oxide basis, of
______________________________________ PbO 10-75 BaO 2-25 Bi.sub.2 O.sub.3 10-85 ZnO 1-10 PbO + Bi.sub.2 O.sub.3 At Least 60 SiO.sub.2 + B.sub.2 O.sub.3 + P.sub.2 O.sub.5 &lt;1 ______________________________________
Optionally, up to 10% individually and up to 20% total of the following oxides may also be included: As.sub.2 O.sub.3, CaO, CdO, GeO.sub.2, HgO, Sb.sub.2 O.sub.3, SrO, TiO.sub.2, Tl.sub.2 O.sub.3, alkali metal oxides, and the colorant or transition metal oxides.
U.S. Pat. No. 3,837,868 is designated to comprise an improvement upon the glasses disclosed in U.S. Pat. No. 3,723,141. Thus, the latter glasses contained Fe.sub.2 O.sub.3 to enhance the stability thereof against devitrification, resulting in compositions consisting essentially, expressed in terms of cation percent on the oxide basis, of
______________________________________ Bi.sub.2 O.sub.3 8-80 PbO + CdO At Least 5% PbO 0-57 Fe.sub.2 O.sub.3 5-32.5 CdO 0-32 ______________________________________
Optionally, up to 15% collectively of compatible glassmaking constituents may also be included in the indicated individual amounts: up to 7.5% BaO and/or ZnO, up to 5% GeO.sub.2, V.sub.2 O.sub.5, NiO, CsO, and other transition metal oxides, and up to 2% B.sub.2 O.sub.3 and/or SiO.sub.2.
Rather than repeating the discussion of the prior art provided in that patent and the review supplied in U.S. Pat. No. 3,723,141, the full disclosures of those patents are specifically incorporated herein by reference.
U.S. application Ser. No. 476,929, filed by us Mar. 21, 1983, under the title LEAD GALLATE GLASSES, discloses glass compositions in the base PbO-Ga.sub.2 O.sub.3 system, to which Bi.sub.2 O.sub.3 is preferably included, capable of transmitting significant infrared radiation to a wavelength of eight microns. The binary glasses consist essentially, in weight percent on the oxide basis, of about 72-85% PbO and 15-28% Ga.sub.2 O.sub.3. The addition of Bi.sub.2 O.sub.3 to the base compositions very substantially improves the melting and forming characteristics thereof, as well as enhancing the stability of the glasses against devitrification. Accordingly, the incorporation of Bi.sub.2 O.sub.3 significantly expands the operable glass compositions to about 10-85% PbO, 5-30% Ga.sub.2 O.sub.3, and up to 80% Bi.sub.2 O.sub.3.
Optionally, up to 30% total of the following compatible metal oxides in the indicated individual proportions may be included:
______________________________________ Cs.sub.2 O 0-20 CuO 0-2 ZnO 0-5 HgO 0-30 CdO 0-12 K.sub.2 O 0-2 Tl.sub.2 O.sub.3 0-20 GeO.sub.2 0-5 In.sub.2 O.sub.3 0-10 Sb.sub.2 O.sub.3 0-10 Na.sub.2 O 0-2 SiO.sub.2 0-2 TeO.sub.2 0-10 Rb.sub.2 O 0-5 ZrO.sub.2 0-5 Cr.sub.2 O.sub.3 0-5 HfO.sub.2 0-5 Nb.sub.2 O.sub.5 0-5 MnO.sub.2 0-5 Al.sub.2 O.sub.3 0-3 Ta.sub.2 O.sub.5 0-5 ______________________________________
It was also observed that the presence of a halogen, preferably chlorine, in an amount of up to about 5% was useful in removing water from the glass, thereby eliminating the strong absorption at a wavelength of about three microns which is characteristic of water in glass.